Memory in .NET - what goes where

The memory slot for a variable is stored on either the stack or the heap. It depends on the context in which it is declared:

1.)Each local variable (ie one declared in a method) is stored on the stack. That includes reference type variables - the variable itself is on the stack, but remember that the value of a reference type variable is only a reference (or null), not the object itself. Method parameters count as local variables too, but if they are declared with the ref modifier, they don't get their own slot, but share a slot with the variable used in the calling code.There's one exception to this simple rule - captured variables (used in anonymous methods) are local in terms of the C# code, but end up being compiled into instance variables in a type associated with the delegate created by the anonymous method.
2.)Instance variables for a reference type are always on the heap. That's where the object itself "lives".
3.)Instance variables for a value type are stored in the same context as the variable that declares the value type. The memory slot for the instance effectively contains the slots for each field within the instance. That means (given the previous two points) that a struct variable declared within a method will always be on the stack, whereas a struct variable which is an instance field of a class will be on the heap.
4.)Every static variable is stored on the heap, regardless of whether it's declared within a reference type or a value type. There is only one slot in total no matter how many instances are created.